The flowmeter of the above-identified patents include a piston that is movable against the force of a spring. The displacement of the piston of the flowmeter is converted to an electric output signal by a potentiometer. As is known, the relationship between the output signal and the displacement of the piston is linear. As it is displaced, the piston of the flowmeter varies the size of a displacement-dependent, variable outlet cross-section, which must be designed such that a linear relationship exists between the displacement of the piston and the flow rate. As a result, the influence of the spring characteristic on the flow rate is compensated. For this reason, a linear relationship exists between the rate of flow and the output signal of the potentiometer. Otherwise the flowmeter would not be suited for use a hydraulic control loop.
The use of such a flowmeter may entail certain disadvantages. In the case of a laminar flow, i.e., low rates of flow, the range of the boundary layer of friction is greater than in the case of a turbulent flow. As a result, the relationship between the quantitative throughput and the output signal becomes nonlinear between the range of low flow rates and the range of higher flow rates due to the discontinuity of the transition from a laminar to a turbulent flow and vice versa. Also, a very strong dependence on viscosity results from temperature fluctuations, and the thereby caused viscosity fluctuations, that occur in operation. Finally, in a flowmeter of the type disclosed in the above referenced patents, wherein a potentiometer is used as the signal generator, the potentiometer itself would have to be made of a conductor, in which the conductance varies over the length. It would be conceivable to direct the output signal of the potentiometer to an intermediate circuit having electronic components which convert the output voltage of the potentiometer one more time such that a nonlinear relationship is produced between the output signal of this intermediate circuit and the displacement of the piston in the flowmeter, in such a manner as to compensate for the nonlinear relationship between the displacement of the piston and the rate of flow.